Organic thin film transistor, flat panel display apparatus comprising the same, and method of manufacturing the organic thin film transistor

ABSTRACT

An organic thin film transistor that can reduce contact resistance between source and drain electrodes and an organic semiconductor layer and can be readily manufactured, a flat panel display apparatus utilizing the organic thin film transistor, and a method of manufacturing the organic thin film transistor. The organic thin film transistor includes: a substrate; a source electrode and a drain electrode disposed on the gate insulating film; a conductive polymer layer disposed to cover at least a portion of each of source and drain electrodes; a hydrophobic material layer disposed on the substrate and the source and drain electrodes except regions where the conductive polymer layer are formed; an organic semiconductor layer electrically connected to the source and drain electrodes; a gate insulating film disposed to cover the organic semiconductor layer; and a gate electrode disposed on the gate insulating film.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 11/546,342, filed Oct. 12, 2006, now U.S. Pat. No. 7,692,185,which claims the benefit of Korean Application No. 10-2005-0100278,filed Oct. 24, 2005, in the Korean Intellectual Property Office, thedisclosures of which are incorporated herein in their entirety byreference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

Aspects of the present invention relate to an organic thin filmtransistor, a flat panel display apparatus comprising the same, and amethod of manufacturing the organic thin film transistor, and moreparticularly, to an organic thin film transistor that has asignificantly reduced contact resistance between source and drainelectrodes and an organic semiconductor layer, and can be easilymanufactured, a flat panel display apparatus having the same, and amethod of manufacturing the organic thin film transistor.

2. Description of the Related Art

Since the development of polyacetylene which is a conjugated organicpolymer having semiconductor characteristics, due to its advantages,such as versatility of synthesis, easy formability into a fiber or afilm, high flexibility, high conductivity, and low cost, many studiesabout transistors using the organic material in functional electronicdevices and optical devices have been performed.

Conventional silicon thin film transistors include a semiconductor layerhaving source and drain regions doped with a high concentration ofdopant and a channel region formed between the source and drain regions,a gate electrode insulated from the semiconductor layer and located on aregion corresponding to the channel region, and source and drainelectrodes which respectively contact the source and drain regions.

However, the conventional silicon thin film transistor having the abovementioned structure has drawbacks in that it requires high manufacturingcosts, is fragile, and is impossible to use with a plastic substratesince the transistor is produced at a high temperature of 300° C. ormore.

Particularly, in flat panel display apparatuses such as a liquid crystaldevice or an organic light emitting diode, thin film transistors areused as switching devices that control operations of each pixel anddriving devices of each of the pixels. To meet the flexibility requiredtogether with the thin and large sizes required in the flat paneldisplay apparatuses, the use of a plastic substrate instead of theconventional glass substrate has been attempted. However, when a plasticsubstrate is used, as described above, a low temperature process must beemployed. Therefore, it is difficult to use the conventional siliconthin film transistors.

However, these problems can be solved when an organic film is used as asemiconductor layer of a thin film transistor. Therefore, recently,studies to use the organic thin film transistor as an organic thin filmtransistor have increased and are now being actively conducted.

However, in the organic thin film transistor, there is a high contactresistance between source and drain electrodes and an organicsemiconductor layer.

That is, unlike a silicon semiconductor layer included in a conventionalsilicon thin film transistor, an organic semiconductor layer included inan organic thin film transistor cannot be doped with a highconcentration. Therefore, there is a high contact resistance betweensource and drain electrodes and an organic semiconductor layer.

SUMMARY OF THE INVENTION

Aspects of the present invention provide an organic thin film transistorthat has a reduced contact resistance between source and drainelectrodes and an organic semiconductor layer and can be easilymanufactured, a flat panel display apparatus having the same, and amethod of manufacturing the organic thin film transistor.

According to an aspect of the present invention, there is provided anorganic thin film transistor comprising: a substrate; a source electrodeand a drain electrode disposed on the substrate; a conductive polymerlayer disposed to cover at least a portion of each of the source anddrain electrodes; a hydrophobic material layer disposed on the substrateand the source and drain electrodes except regions where the conductivepolymer layer is formed; an organic semiconductor layer electricallyconnected to the source and drain electrodes; a gate insulating filmdisposed to cover the organic semiconductor layer; and a gate electrodedisposed on the gate insulating film.

According to another aspect of the present invention, there is providedan organic thin film transistor comprising: a substrate; a gateelectrode disposed on the substrate; a gate insulating film covering thegate electrode; a source electrode and a drain electrode disposed on thegate insulating film; a conductive polymer layer disposed to cover atleast a portion of each of the source and drain electrodes; ahydrophobic material layer disposed on the substrate and the source anddrain electrodes except for regions where the conductive polymer layeris formed; and an organic semiconductor layer electrically connected tothe source and drain electrodes.

While not required in all aspects, the conductive polymer layer may bedisposed to cover an edge of the source electrode in a drain electrodedirection and an edge of the drain electrode in a source electrodedirection. While not required in all aspects, the conductive polymerlayer may be disposed to cover the source and drain electrodes. Whilenot required in all aspects, the source and drain electrodes may betransparent electrodes. While not required in all aspects, the sourceand drain electrodes may be formed of indium tin oxide (ITO), indiumdoped zinc oxide (IZO), zinc oxide (ZnO), or indium oxide (In₂O₃).

While not required in all aspects, the hydrophobic material layer may beformed of a surface treatment agent that has a self-assembled monolayerincluding silane moiety having 1-3 reactive halogen atoms or alkoxymoieties, and including 1-3 hydrophobic moieties. While not required inall aspects, the hydrophobic material layer may be formed of a surfacetreatment agent that has a hydrophobic self-assembled monolayer having atrichlorosilanyl moiety or a trialkoxysilanyl moiety at the end thereof.While not required in all aspects, the hydrophobic material layer may beformed of octadecyltrichlorosilane (OTS). While not required in allaspects, the conductive polymer layer may be formed of polyethylenedioxythiophene (PEDOT) or polyaniline (PANI).

According to another aspect of the present invention, there is provideda flat panel display apparatus having an organic thin film transistordescribed above. According to another aspect of the present invention,there is provided a method of manufacturing an organic thin filmtransistor, comprising: forming source and drain electrodes on asubstrate; forming a hydrophobic material layer covering the source anddrain electrodes on an entire surface of the substrate; removing thehydrophobic material layer at least on a region of each of the sourceand drain electrodes; forming a conductive polymer layer on regionswhere the hydrophobic material layer is removed; forming an organicsemiconductor layer to be electrically connected to the source and drainelectrodes; forming a gate insulating film covering the organicsemiconductor layer; and forming a gate electrode on the gate insulatingfilm.

According to another aspect of the present invention, there is provideda method of manufacturing an organic thin film transistor, comprising:forming a gate electrode on a substrate; forming a gate insulating filmcovering the gate electrode; forming source and drain electrodes on thegate insulating film; forming a hydrophobic material layer covering thesource and drain electrodes on an entire surface of the substrate;removing the hydrophobic material layer at least on a region of each ofthe source and drain electrodes; forming a conductive polymer layer onregions where the hydrophobic material layer is removed; and forming anorganic semiconductor layer to be electrically connected to the sourceand drain electrodes.

While not required in all aspects, the removing of the hydrophobicmaterial layer may be removing the hydrophobic material layer on an edgeof the source electrode in a drain electrode direction and removing thehydrophobic material layer on an edge of the drain electrode in a sourceelectrode direction. While not required in all aspects, the removing ofthe hydrophobic material layer may be removing the hydrophobic materiallayer on the source electrode and removing the hydrophobic materiallayer on the drain electrode. While not required in all aspects, thesource electrode or the drain electrode may be formed of a transparentmaterial. While not required in all aspects, the source electrode or thedrain electrode may be formed of ITO, IZO, ZnO, or In₂O₃.

While not required in all aspects, the hydrophobic material layer may beformed of a surface treatment agent that has a self-assembled monolayerincluding silane moiety having 1-3 reactive halogen atoms or alkoxymoieties, and including 1-3 hydrophobic moieties. While not required inall aspects, the hydrophobic material layer may be formed of a surfacetreatment agent that has a hydrophobic self-assembled monolayer having atrichlorosilanyl moiety or a trialkoxysilanyl moiety at the end thereof.While not required in all aspects, the hydrophobic material layer may beformed of OTS.

While not required in all aspects, the conductive polymer layer may beformed of PEDOT or PANI. While not required in all aspects, the formingof the hydrophobic material layer may be performed using a spin coatingmethod or a dipping method. While not required in all aspects, theremoving of the hydrophobic material layer may be performed byirradiating a laser beam onto regions where the hydrophobic materiallayer is removed.

While not required in all aspects, the forming of the conductive polymerlayer may be performed using a spin coating method, a dipping method, oran inkjet printing method. While not required in all aspects, theforming of the conductive polymer layer may comprise: forming theconductive polymer layer in regions on the source and drain electrodeswhere the hydrophobic material layer is removed using a spin coatingmethod, a dipping method, or an inkjet printing method; and removing theconductive polymer layer remaining on a region between the source anddrain electrodes.

While not required in all aspects, the removing of the conductivepolymer layer remaining on a region between the source and drainelectrodes may be performed by irradiating a laser beam, ultravioletrays, or an electron beam onto the region between the source and drainelectrodes.

Additional aspects and/or advantages of the invention will be set forthin part in the description which follows and, in part, will be obviousfrom the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the invention will becomeapparent and more readily appreciated from the following description ofthe embodiments, taken in conjunction with the accompanying drawings ofwhich:

FIGS. 1 through 4 are cross-sectional views illustrating a process ofmanufacturing an organic thin film transistor according to an embodimentof the present invention;

FIG. 5 is a cross-sectional view of a modified organic thin filmtransistor from the organic thin film transistor of FIG. 4 according toan embodiment of the present invention;

FIG. 6 is a cross-sectional view of another modified organic thin filmtransistor from the organic thin film transistor of FIG. 4 according toan embodiment of the present invention;

FIG. 7 is a cross-sectional view of another modified organic thin filmtransistor from the organic thin film transistor of FIG. 4 according toan embodiment of the present invention;

FIGS. 8 through 10 are cross-sectional views illustrating a method ofmanufacturing an organic thin film transistor according to anotherembodiment of the present invention; and

FIG. 11 is a cross-sectional view of a flat panel display apparatusaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The embodiments are described below in order to explain thepresent invention by referring to the figures.

FIGS. 1 through 4 are cross-sectional views illustrating a process ofmanufacturing an organic thin film transistor according to an embodimentof the present invention. Referring to FIG. 1, a source electrode 23 anda drain electrode 24 are formed on a substrate 10. A hydrophobicmaterial layer 25 covering the source electrode 23 and the drainelectrode 24 is formed on an entire surface of the substrate 10. Thesubstrate 10 can be a glass substrate, a plastic substrate such as anacryl substrate, or a metal plate substrate. Of course, the substrateincluded in the organic thin film transistor according to the presentembodiment is not limited thereto.

The source and drain electrodes 23 and 24 can be formed by various wayson the substrate 10 using various conductive materials, for example, bypatterning a conductive layer deposited on an entire surface of thesubstrate 10, depositing patterned source and drain electrodes on apredetermined region of the substrate using a mask, or using an inkjetprinting method.

As will be described later, the organic thin film transistor can beincluded in a pixel unit of a flat panel display apparatus. In such acase, the source electrode 23 or the drain electrode 24 of the organicthin film transistor is electrically coupled to one electrode of eachpixel. At this time, if necessary, the source electrode 23 or the drainelectrode 24 of the organic thin film transistor and the coupledelectrode of the pixel can be formed as a single body. In this case,when the pixel electrode must be transparent, the source electrode 23 orthe drain electrode 24 also can be formed of a transparent material. Thetransparent material can be ITO, IZO, ZnO, In₂O₃, etc.

The hydrophobic material layer 25 is formed on an entire surface of thesubstrate 10 to cover the source electrode 23 and the drain electrode24. The hydrophobic material layer 25 may be formed of a surfacetreatment agent that has a self-assembled monolayer including silanemoiety having 1-3 reactive halogen atoms or alkoxy moieties, and 1-3hydrophobic moieties, and particularly, a surface treatment agent mayhave a hydrophobic self-assembled monolayer having a trichlorosilanylmoiety or a trialkoxysilanyl moiety at the end thereof. Such a surfacetreating agent can be octadecyltrichlorosilane (OTS). Since thehydrophobic material layer 25 is formed on the entire surface of thesubstrate 10, the hydrophobic material layer 25 can be readily formedusing a spin coating method or a dipping method.

After the hydrophobic material layer 25 is formed, at least a portion ofthe hydrophobic material layer 25 on each of the source electrode 23 andthe drain electrode 24 is removed. For example, as depicted in FIG. 1,the hydrophobic material layer 25 can be removed by irradiating a laserbeam onto a region where the hydrophobic material layer 25 is to beremoved. There are various methods to irradiate a laser beam onto aregion where the hydrophobic material layer 25 is to be removed. Forexample, as depicted in FIG. 1, a photomask 40 formed of a shieldingmaterial 42 in a predetermined pattern that blocks transmission of thelaser beam that is formed on a transparent plate 41 can be used.

Referring to FIG. 2, a portion of the hydrophobic material layer 25 oneach of the source electrode 23 and the drain electrode 24 is removed,and thus a portion of each of the source electrode 23 and the drainelectrode 24 is exposed through openings 25 a formed in the hydrophobicmaterial layer 25.

Referring to FIG. 3, afterward, a conductive polymer layer 26 is formedin each of the regions 25 a on the source electrode 23 and the drainelectrode 24 where the hydrophobic material layer 25 is removed. Theconductive polymer layer 26 can be formed of various materials, forexample, polyethylene dioxythiophene (PEDOT) or polyaniline (PANI).

The conductive polymer layer 26 can be formed using various methods suchas an inkjet printing method. In particular, the use of a dipping methodor a spin coating method is advantageous in view of simplifying theprocessing and reducing manufacturing time. That is, due to thecharacteristics of the hydrophobic material layer 25, a conductivepolymer layer does not form on the hydrophobic material layer 25.Accordingly, when the dipping method or the spin coating method is used,the conductive polymer layer 26 is naturally formed only on the sourceelectrode 23 and the drain electrode 24 where the hydrophobic materiallayer 25 is not present.

When the manufacture of an organic thin film transistor is completed, achannel is formed between the source electrode 23 and the drainelectrode 24 according to predetermined conditions. For this purpose,when the conductive polymer layer 26 is formed, a conductive polymermaterial should not remain between the source electrode 23 and the drainelectrode 24. Of course, the conductive polymer material layer cannot beformed between the source electrode 23 and the drain electrode 24 wherethe hydrophobic material layer 25 is present, but in some cases, theconductive polymer material can remain. Accordingly, an operation forremoving the conductive polymer material remaining in a region betweenthe source electrode 23 and the drain electrode 24 can further beincluded at this time. For example, the conductive polymer material canbe readily removed by irradiating a laser beam, ultraviolet rays, or anelectron beam onto the region between the source electrode 23 and thedrain electrode 24.

Referring to FIG. 4, the manufacture of an organic thin film transistoris completed by forming an organic semiconductor layer 27 electricallyconnected to the source electrode 23 and the drain electrode 24, a gateinsulating film 22 covering the organic semiconductor layer 27, and agate electrode 21 on the gate insulating film 22.

The organic semiconductor layer 27 is formed of an organic materialhaving semiconductor characteristics, for example, including at leastone of pentacene, tetracene, anthracene, naphthalene, alpha-6-thiophene,alpha-4-thiophene, perylene and its derivatives, rubrene and itsderivatives, coronene and its derivatives, perylene tetracarboxylicdiimide and its derivatives, perylene tetracarboxylic dianhydride andits derivatives, polythiophene and its derivatives,polyparaphenylenevinylene and its derivatives, polyparaphenylene and itsderivatives, polyplorene and its derivatives, polythiopenevinylene andits derivatives, polythiophene-hetero ring aromatic copolymer and itsderivatives, oligoacen of naphthalene and its derivatives,alpha-5-thiophene oligothiophene and its derivatives, phthalocianin thatdoes not include a metal and its derivatives, phyromeliticdianhydrideand its derivatives, phyromelitic diimid and its derivatives,perrylenetetracarboxy acid dianhydride and its derivatives, andperrylenetetracarboxilic diimid and its derivatives. The organicsemiconductor layer 27 can be formed using various methods such as aninkjet printing method, a dipping method, a spin coating method, etc.

The gate insulating film 22 can be formed of an inorganic material suchas a silicon oxide or a silicon nitride, or an organic material such asparylene, epoxy, PVC, BCB, or CYPE to improve flexibility of the thinfilm transistor after the manufacturing of the thin film transistor iscompleted.

As described above, there is a problem of low on-current flow and lowon/off ratio of an organic thin film transistor due to the high contactresistance between the source and drain electrodes 23 and 24 and theorganic semiconductor layer 27. Therefore, by interposing the conductivepolymer layer 26 between the source and drain electrodes 23 and 24 andthe organic semiconductor layer 27, a potential barrier caused by anenergy difference between a fermi level of the source and drainelectrodes 23 and 24 and a highest occupied molecular orbit (HOMO)energy level or a lowest unoccupied molecular orbit (LUMO) energy levelof the organic semiconductor layer 27 can be reduced. As a result, thecharacteristics of the organic thin film transistor can be significantlyimproved by reducing the contact resistance between the source and drainelectrodes 23 and 24 and the organic semiconductor layer 27.

FIG. 5 is a cross-sectional view of a modified organic thin filmtransistor from the organic thin film transistor of FIG. 4 according toan embodiment of the present invention. In the organic thin filmtransistor depicted in FIG. 4, the openings 25 a (refer to FIG. 2)formed in the hydrophobic material layer 25 are respectively formed onregions corresponding to a central portion of the source and drainelectrodes 23 and 24. Accordingly, the conductive polymer layer 26 isrespectively formed on the central portion of the source and drainelectrodes 23 and 24. The source and drain electrodes 23 and 24 areelectrically connected to each other according to predeterminedelectrical signals applied to the gate electrode 21 through a channelformed in the organic semiconductor layer 27. At this time, as describedabove, the source and drain electrodes 23 and 24 may be electricallyconnected to each other through the conductive polymer layer 26 formedon the source and drain electrodes 23 and 24 to reduce contactresistance between the source and drain electrodes 23 and 24 and theorganic semiconductor layer 27.

Accordingly, as depicted in FIG. 5, the conductive polymer layer 26 maybe formed in a shape covering an edge portion of the source electrode 23in a drain electrode 24 direction, and an edge portion of the drainelectrode 24 in a source electrode 23 direction. Here, the edge portionincludes an end portion. The conductive polymer layer 26 can be formedin various ways. For example, the conductive polymer layer 26 can beformed in a shape covering an end portion of the source electrode 23 ina drain electrode direction and an end portion of the drain electrode 24in a source electrode direction as depicted in FIG. 6. Also, as depictedin FIG. 7, the conductive polymer layer 26 can be formed to cover thesource and drain electrodes 23 and 24.

FIGS. 8 through 10 are cross-sectional views illustrating a process ofmanufacturing an organic thin film transistor according to anotherembodiment of the present invention. The organic thin film transistorsaccording to embodiments of the present invention and modifiedembodiments are staggered organic thin film transistors in which thegate electrode is formed over source and drain electrodes and an organicsemiconductor layer is formed on the source and drain electrodes in eachembodiment, but the present invention is not limited thereto. Forexample, aspects of the present invention can also be applied to aninverted coplanar organic thin film transistor in which source and drainelectrodes are formed over a gate electrode and an organic semiconductorlayer is formed on the source and drain electrodes.

That is, referring to FIG. 8, a gate electrode 21 is formed on asubstrate 10, a gate insulating film 22 covering the gate electrode 21is formed, source and drain electrodes 23 and 24 are formed on the gateinsulating film 22, and a hydrophobic material layer 25 covering thesource and drain electrodes 23 and 24 is formed on an entire surface ofthe substrate 10. Afterward, as depicted in FIG. 9, openings 25 a areformed to expose a portion of each of the source and drain electrodes 23and 24 by removing at least a portion of the hydrophobic material layer25 on each of the source and drain electrodes 23 and 24 using any one ofvarious methods such as the irradiation of a laser beam using aphotomask 40 as depicted in FIG. 8. Afterward, a conductive polymerlayer 26 is formed on the source and drain electrodes 23 and 24 wherethe hydrophobic material layer 25 is removed. Next, an organicsemiconductor layer 27, electrically connected to the source and drainelectrodes 23 and 24, is formed. As a result, an inverted coplanar typeorganic thin film transistor as depicted in FIG. 10 is manufactured.

FIG. 11 is a cross-sectional view of a flat panel display apparatusaccording to an embodiment of the present invention. As described above,due to its high flexibility, the organic thin film transistors can beused for various flexible flat panel display apparatuses having a thinfilm transistor. The flat panel display apparatus includes variousdisplay apparatuses such as a liquid crystal display apparatus and anorganic light emitting diode. Here, an organic light emitting displayapparatus having an organic thin film transistor as described above willnow be briefly described with reference to FIG. 11.

In a light emitting display apparatus having organic thin filmtransistors according to various embodiments of the present invention,the organic thin film transistor and the light emitting diode areincluded on a substrate 110. Various organic light emitting displayapparatuses can be applied to aspects of the present invention. Theorganic light emitting display apparatus according to an embodiment ofthe present invention is an active matrix (AM) light emitting displayapparatus having an organic thin film transistor.

Referring to FIG. 11, each of the sub-pixels includes at least oneorganic thin film transistor. A buffer layer (not shown) can be formedon the substrate 110 using SiO₂, if necessary, and an organic thin filmtransistor as described above is included on the buffer layer. Ofcourse, the organic thin film transistor depicted in FIG. 11 is one ofthe various organic thin film transistors according to embodiments andmodified embodiments of the present invention, however the presentinvention is not limited thereto.

A passivation film 128 is formed on the organic thin film transistorusing SiO₂, and a pixel defining film 129 is formed on the passivationfilm 128 using acrylic or polyimide compound. The passivation film 128serves as a protection film that protects the organic thin filmtransistor and serves as a planarizing film that planarizes an uppersurface thereof.

Although not shown, at least one capacitor can be connected to theorganic thin film transistor. A circuit that includes the organic thinfilm transistor is not necessarily limited to the circuit depicted inFIG. 11, but can have various modifications.

An organic light emitting diode is connected to a drain electrode 124.The organic light emitting diode includes an intermediate layer 133 thatincludes a pixel electrode 131, a facing electrode 134, and at least onelight emitting layer interposed between the pixel electrode 131 and thefacing electrode 134. The facing electrode 134 can have various forms,for example, the facing electrode 134 can be formed in common to aplurality of pixels.

In FIG. 11, for convenience of explanation of the structure of thesub-pixel, the intermediate layer 133 is patterned to correspond to thesub-pixel, but the intermediate layer 133 can be formed in one unit withan intermediate layer of an adjacent sub-pixel. Also, the intermediatelayer 133 can be formed in various ways, for example, a portion of theintermediate layer 133 can be formed in each sub-pixel and the otherportion of the intermediate layer 133 can be formed in one unit with anintermediate layer of an adjacent sub-pixel.

The pixel electrode 131 functions as an anode electrode and the facingelectrode 134 functions as a cathode electrode, but the polarity of thepixel electrode and the facing electrode may be reversed. The pixelelectrode 131 can be formed as a transparent electrode or a reflectionelectrode. When the pixel electrode 131 is formed as a transparentelectrode, the pixel electrode 131 can be formed of ITO, IZO, ZnO orIn₂O₃, and when the pixel electrode 131 is formed as a reflectionelectrode, the pixel electrode 131 can be formed of ITO, IZO, ZnO orIn₂O₃ on a reflection film after forming the reflection film using Ag,Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, or a compound of these metals.

The facing electrode 134 can be formed as a transparent electrode or areflection electrode. When the facing electrode 134 is formed as atransparent electrode, after depositing a metal having a low workfunction, such as Li, Ca, LiF/Ca, LiF/Al, Al, Ag, Mg, or a compound ofthese metals on the intermediate layer 133, an auxiliary electrode layeror a bus electrode line formed of a material for forming the transparentelectrode, such as ITO, IZO, ZnO or In₂O₃, can be included on thematerial layer. When the facing electrode 134 is formed as a reflectionelectrode, the facing electrode 134 is entirely formed by depositing Li,Ca, LiF/Ca, LiF/Al, Al, Ag, Mg, or a compound of these metals.

The intermediate layer 133 included between the pixel electrode 131 andthe facing electrode 134 can be formed of a small molecular weightorganic material or a polymer organic material. When the intermediatelayer 133 is formed of a small molecular weight organic material, theintermediate layer 133 can be formed in a single or a compositestructure by stacking a hole injection layer (HIL), a hole transportlayer (HTL), an emission layer (EML), an electron transport layer (ETL),and an electron injection layer (EIL). Organic materials that can beused for forming the intermediate layer include copper phthalocyanine(CuPc), N,N′-Di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB), andtris-8-hydroxyquinoline aluminum (Alq3), but the present invention isnot limited thereto. Small molecular weight organic material layers canbe formed by a vacuum evaporation method using masks.

When the intermediate layer 133 is formed of a polymer organic material,the intermediate layer 133 can have a structure that includes an HTL andan EML. The polymer HTL can be formed of poly-(2,4)-ethylene-dihydroxythiophene (PEDOT), and the light emitting layer can be formed ofpoly-phenylenevinylene (PPV) and polyfluorene group polymers.

An organic light emitting diode formed on the substrate 110 is sealed bya facing member (not shown). The facing member, like the substrate 110,can be formed of glass, plastic, or metal.

An organic light emitting display apparatus that can realize correctimages according to inputted signals can be manufactured by includingorganic thin film transistors according to embodiments and modifiedembodiments of the present invention. Also, aspects of the presentinvention have been described mainly with regard to the structure of anorganic light emitting display apparatus, but any display apparatus thatincludes an organic thin film transistor can be applied to the presentinvention.

An organic thin film transistor, a flat panel display apparatus havingthe organic thin film transistor, and a method of manufacturing theorganic thin film transistor according to aspects of the presentinvention can provide the following and/or other advantages. First,contact resistance between source and drain electrodes and an organicsemiconductor layer can be greatly reduced by including a conductivepolymer layer between the source and drain electrodes and the organicsemiconductor layer. Second, the conductive polymer layer can be formedexclusively between the source and drain electrodes and the organicsemiconductor layer at low costs by employing a hydrophobic materiallayer. Third, the flexibility of a flat panel display apparatus canfurther be increased by including organic thin film transistors havingimproved characteristics.

Although a few embodiments of the present invention have been shown anddescribed, it would be appreciated by those skilled in the art thatchanges may be made in this embodiment without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

1. A method of manufacturing an organic thin film transistor,comprising: forming source and drain electrodes; forming a hydrophobicmaterial layer covering the source and drain electrodes on an entiresurface of a layer on which the source and drain electrodes are formed;removing the hydrophobic material layer at least on a region of each ofthe source and drain electrodes; forming a conductive polymer layer onregions where the hydrophobic material layer is removed; and forming anorganic semiconductor layer to be electrically connected to the sourceand drain electrodes.
 2. The method of claim 1, wherein the removing ofthe hydrophobic material layer comprising removing the hydrophobicmaterial layer on an edge of the source electrode in a drain electrodedirection and removing the hydrophobic material layer on an edge of thedrain electrode in a source electrode direction.
 3. The method of claim1, wherein the removing of the hydrophobic material layer comprisingremoving the hydrophobic material layer on the source electrode andremoving the hydrophobic material layer on the drain electrode.
 4. Themethod of claim 1, wherein one of the source electrode, the drainelectrode and combination thereof is formed of a transparent material.5. The method of claim 4, wherein one of the source electrode, the drainelectrode and a combination thereof is formed of ITO, IZO, ZnO, orIn₂O₃.
 6. The method of claim 1, wherein the hydrophobic material layeris formed of a surface treatment agent that has a self-assembledmonolayer including silane moiety having 1-3 reactive halogen atoms oralkoxy moieties, and including 1-3 hydrophobic moieties.
 7. The methodof claim 6, wherein the hydrophobic material layer is formed of asurface treatment agent that has a hydrophobic self-assembled monolayerhaving a trichlorosilanyl moiety or a trialkoxysilanyl moiety at an endthereof.
 8. The method of claim 7, wherein the hydrophobic materiallayer is formed of OTS.
 9. The method of claim 1, wherein the conductivepolymer layer is formed of PEDOT or PANI.
 10. The method of claim 1,wherein the forming of the hydrophobic material layer is performed usinga spin coating method or a dipping method.
 11. The method of claim 1,wherein the removing of the hydrophobic material layer comprisesirradiating a laser beam onto regions where the hydrophobic materiallayer is removed.
 12. The method of claim 1, wherein the forming of theconductive polymer layer comprises using a spin coating method, adipping method, or an inkjet printing method.
 13. The method of claim 1,wherein the forming of the conductive polymer layer comprises: formingthe conductive polymer layer in regions on the source and drainelectrodes where the hydrophobic material layer is removed using a spincoating method, a dipping method, or an inkjet printing method; andremoving the conductive polymer layer remaining on a region between thesource and drain electrodes.
 14. The method of claim 13, wherein theremoving of the conductive polymer layer remaining on a region betweenthe source and drain electrodes comprises irradiating a laser beam,ultraviolet rays, or an electron beam onto the region between the sourceand drain electrodes.
 15. The method of claim 1, further comprising:forming a gate insulating film covering the organic semiconductor layer;and forming a gate electrode on the gate insulating film.
 16. The methodof claim 1, prior to forming the source and drain electrodes, furthercomprising: forming a gate electrode; and forming a gate insulating filmcovering the gate electrode, wherein the source and drain electrodes areformed on the gate insulating film.